Catalyst system for activating surfaces prior to electroless deposition

ABSTRACT

An electroless metal plating catalyst and a particular method of preparing it at elevated temperature by reaction of a stannous salt and palladous or other similar catalytic metal ion augmented by incorporating a booster compound are disclosed. The resultant catalyst is useable at much lower catalytic metal concentration in plating operations than conventional prior catalysts. The booster compounds employed are acid or alkali soluble metal salts forming a sparingly soluble compound when contacted with conventional alkali or acid accelerators in the plating process.

United States Patent [191 Rantell et al.

[4 1 Sept. 2, 1975 CATALYST SYSTEM FOR ACTIVATING SURFACES PRIOR TOELECTROLESS DEPOSITION [75] Inventors: Alan Rantell, London, England;Abraham Holtzman, Bat-Yam,

Israel [73] Assignee: MacDermid Incorporated,

Waterbury, Conn.

22 Filed: Oct. 4, 1973 21 Appl.No.:403,502

[30] Foreign Application Priority Data Mar. 21, 1973 United Kingdom13545/73 [52] US. Cl. 106/1; 1 17/47 A; 204/30 [51] Int. Cl. C23C 3/00[58] Field of Search 106/1; 204/30; 117/47 A;

[56] References Cited UNITED STATES PATENTS 3,532,518 lO/l97O DOttavio204/30 X 3,650,913 3/1972 DOttavio 204/30 3,698,919 10/1972 Kuzmik..204/3OX Primary ExaminerLewis T. Jacobs Attorney, Agent, orFirmSteward & Steward 57 ABSTRACT compound when contacted withconventional alkali or acid accelerators in the plating process.

8 Claims, No Drawings CATALYST SYSTEM FOR ACTIVATING SURFACES PRIOR TOELECTROLESS DEPOSITION CROSS REFERENCE TO PRIOR RELATED APPLICATIONSThis application corresponds to British Provisional Specification No.13545/73, filed Mar. 21, 1973.

FIELD OF THE INVENTION The present invention relates to the preparationand use of a catalyst composition for activating nonconductive surfacesprior to electroless deposition of metals.

For the purpose of electroless or chemical plating of non-conductivesubstrates, small quantities of activator or catalyst must first beplaced on the surface of the substrate. Palladium is found to be themost satisfactory catalyst but any metal selected from palladium, gold,silver or the platinum group of metals is suitable.

The activating or catalyzing process is often carried out by consecutiveimmersion of the substrate in solutions containing PdCl and SnClrespectively. More recently the use of single step activators comprisingcolloidal mixtures of PdCl and SnCl has been proposed. Typical workingstrength catalyst solutions contain:

PdCI. 300- lUUOmg/I SnCL |s SOg/l wt sno smo 1 7 g/l HCl 250- 3(J0ml/lHowever, these PdCl- /sncl mixtures are more effective when used inconjunction with an additional treatment solution known as anaccelerator. Accelerators are generally solutions of strong acids orstrong alkalis and are employed between the catalyst treatment andelectroless deposition.

The method and conditions of preparation of PdCIg/SIICI- mixtures iscritical. Further, the high con ccntration of PdCIg employed makes thecatalyst solutions very expensive. Less critical yet cheaper solutionswould be an advantage.

SUMMARY OF THE INVENTION The principle of the invention involves theformation of a highly active compound by reaction at high temperaturebetween a stannous salt, usually the chloride, and low concentrations ofpalladous or other similar catalytic ions; e.g. Au(l), Au( III), Pt(II),Pt(IV), Rh(IIl), Ru(IlI), Ru(IV), Os(III), Os(IV), Ir(III), Ir- (IV) orAg(l). The choice of booster compound is determined by the nature of theaccelerator solution employed in the processing cycle. It is essentialthat the 5 booster compound should form a sparingly soluble compoundwhen contacted with the accelerator; i.e. if a NaOH accelerator isemployed, the booster com pound should be an acid salt of metalion-forming insoluble hydroxides at alkaline pH values; e.g. compoundscontaining Mg, Fe, Fe, Mn, Cu, Ni, Co or Cr.

In one method of implementing the present invention, the catalyst isformed by heating the component supplying the catalytic ion and thebooster compound in strong acid solution at temperatures in excess of75C, and then adding an excess of stannous ion. The temperature of themixture is maintained above 75C until the reaction is completed. Duringthe reaction, the color of the mixture changes from light amber to darkbrown, returning to light amber. Finally the completion of the reactionis indicated when the color of the mixture becomes dark brown for thesecond time.

This may take from 1 to 20 minutes.

Alternatively the stannous ion may be added in two stages. Sufficientstannous salt to carry out the reaction is first added to the mixture ofcatalytic ion and booster compound at temperatures in excess of C. Thequantity required may be between 2 and 50 g/l as SnCl depending ontemperature and concentration of catalytic ion. When the reaction iscomplete after 1-20 minutes, a vast excess of an acid stannous salt isadded. Small quantities of sodium stannate are found useful forstabilizing the compound formed between Sn(II) and the catalytic ion,e.g. (Pd(II)).

The preheating of the reactants to temperatures in excess of 75C priorto admixing them in the preparation step is an important part of theinvention. The catalytic activity of the reaction product formed betweenSn(II) and the catalytic ion, e.g. Pd(II), increases with increase ofreaction temperature during manufacture, allowing relatively lowconcentrations of catalytic ion to be used. At temperatures below 75Cmuch greater concentrations of catalytic ion are required in order tomaintain catalytic activity; viz. greater than 150 mg/l of PdCl Thereaction between Sn(II) and Pd(II), i.e. the catalytic ion, may take tworoutes. The preferred reac tion yields a Sn(II)/Pd(ll) addition compoundwhereas a secondary reaction causes formation of metallic palladium. Thelatter reaction is generally undesirable. The use of high manufacturingtemperatures and excess stannous salt encourages the preferred reactionand inhibits the secondary reaction. V

The invention is illustrated by the following examples for thepreparation and use of the catalyst.

EXAMPLE I For 1 liter of working strength catalyst a mixture containing:

PdCl 45 mg. MnCl. 15 g.

HCl (37% w/v) 200 ml. H. ,O 400 ml.

is heated to.90C and reacted with a solution containing:

SnCI 2H O 150 g. Na- SnO 3H- 4 g. HCl (3771 w/v) 300 ml.

The temperature is maintained at C for 15 minutes and then allowed tocool prior to use.

The catalyst may be used to activate plastic surfaces or copper cladprinted circuit boards prior to electroless deposition. For the platingof ABS plastics the following processing cycle is preferred:

ABS plastic is etched in a mixture containing 200-400 g/l CrO and 300600g/l H 50 at 4070C for 2l0 minutes. After thorough rinsing, the plasticis immersed in the catalyst solution for l-5 minutes at 5 roomtemperature. For increased activation it is perg/l NaOH for lminutes at20-60C. The preferred temperature of the accelerator is 40C. Theactivated plastic is then immersed in any electroless nickel or copperplating solution. A preferred composition is:

pH adjusted to 8.0 8.5 with NH.

The electroless nickel solution is employed at 20-30C for 5-l0 minutes.

EXAMPLE 2 For 1 liter of working strength catalyst a mixture containing:

Pd(l 45 mg. FeCl 40 g.

HCl (37% w/v) 200 ml. H. 400 ml.

is heated to 90C and then reacted with 20g SnCl .2H-,O. After thereaction has continued for a period of minutes, a mixture containing:

The time allowed for the reaction of the first addition is not criticaland may be for any period greater than 1 minute, but 15 minutes ispreferred. The reaction temperature again is important, as it must begreater than 75C, 90-95C being preferred.

The catalyst solution may be used to activate plastic surfaces in themanner described in Example 1.

EXAMPLE 3 The catalyst is prepared and used-as in Example 1 except thatin this instance the PdCl is replaced by 75 mg of HAu Cl EXAMPLE 4 For 1liter of working strength catalyst a mixture containing:

Pdcl 40 mg. AICL, g.

HCI (37% w/ 200 ml. up 400 ml.

is heated to 90C and reacted with a solution containing:

The temperature of the mixture is maintained at 90C for IS minutes andthen cooled to room temperature for use. The electroless platingprocedure then proceeds in a similar manner to that described in ExampleI, except that in this instance the accelerator solution should be l0500ml/] of ammonia solution (28% w/v).

In this example AICL, acts as a booster compound when used inconjunction with an ammonium hydrox- LII idc accelerator since Al(OH) isnot soluble in ammonia solution.

EXAMPLE 5 For 1 liter of working strength catalyst a mixture containing:

PdCl- 45 mg. BaCl 40 g.

HCl (37% w/v) 200 ml. H 0 400 ml.

is heated to 90C and reacted with a solution containing:

The temperature of the mixture is maintained at 90C for 15 minutes andthen the catalyst is cooled at room temperature for use.

The catalyst solution may be used to activate plastic Surfaces in asimilar manner to that described in Example 1, except that in thisinstance the accelerator solution should be 10-200 g/l H 50 Theactivated catalysts referred to in the invention are not colloidal innature. Tyndall effect measurements taken on the undiluted catalystsolutions and electron microscopy of the adsorbed catalyst fail to showany colloidal particles. The active component of the snCl /Pdcl catalystis an acid soluble complex formed between Sn(ll) and Pd(ll). On contactwith the accelerator solution, a slow redox reaction occurs:

Sn(-ll) Pd(lll) Sn(lV) Pd(O).

The elemental palladium formed can then initiate electroless deposition.The presence of the booster enables a concentration of catalytic metalion in solution equivalent to about 10 mg/l of Pd as PdCl to beeffective. For economic reasons a concentration equivalent to about 500mg/] of PdCl represents a practical maximum.

Booster compounds such as MnCl and FeCl;, produce a voluminous surfaceprecipitate when the adsorbed catalyst contacts the sodium hydroxideaccelerator. The precipitated metal hydroxides help to retain the Pd(ll)on the plastic surface until the redox reaction has occurred. If nobooster compound is used the Pd(ll) may leach into the acceleratorbefore any reaction has occurred.

What is claimed is:

l. A method for preparing a catalyst solution by heating an acidsolution of a Pd(ll) catalytic ion wherein said catalytic ion is presentin amount sufficient to provide in the working strength catalystsolution a concentration equivalent to about 10500 mg/l of Pd as PdCI-with a solution containing a stochiometric excess of stannous saltwherein at least one of said catalytic ion and stannous salt solutionsis first heated to a temperature in excess of C before the other isadded to it, and wherein a booster compound consisting of a solublemetal salt, of which the cation is capable of forming a precipitate whencontacted with the accelerator solution used in an electroless platingprocess, is added to the catalyst mixture during preparation, saidbooster compound being present in amount of about 0.] mol/l up to 5mol/l in the working strength solution.

2. A method for preparing a catalyst as in claim 1, for use in anelectroless plating process employing as the accelerator a strongalkali, wherein the booster compound is a salt containing a cationselected from the group consisting of Mg, Fe, Fe. Mn, Mn, Cu, Ni, Co,Cr.

3. A method for preparing a catalyst as in claim 1, for use in anelectroless plating process employing as the accelerator an alkalineammonia solution, wherein the booster compound is a salt containing acation selected from the group consisting of Mg, Fe. Mn'. Mn, zu: Pb2+AliH 4. A method for preparing a catalyst as in claim 1, for use in anelectroless plating process employing as the accelerator sulphuric acidor a soluble acid sulphate, wherein the booster compound is a saltcontaining a cation selected from the group consisting of Ca Ba, Sr, Pb.

5. A method for preparing a catalyst as in claim 1, for use in anelectroless plating process employing as the accelerator a solublecarbonate or phosphate, wherein the booster compound is a saltcontaining a cation selected from the group consisting of Ca Ba, Sr,Pb'l't', Mgl-i" F ll+q 11 3+g M 2+, M 3+ C 2+, bJiZ-i-q CO2+, c 3+qCd2+s 2 2+g l)b.l-l-s Alli-F 6. A method for preparing a catalyst as inclaim 1, for use in an electroless plating process employing as theaccelerator a soluble fluoride, wherein the booster compound is saltcontaining a cation selected from the group consisting of Mg, Ca, Ba,Sr, Zn, Cd, Al3+ Pb2+ M l-F, M 3+ 7. An aqueous acid catalyst solutioncomprising a Pd(ll) catalytic ion wherein said catalytic ion is presentin amount sufficient to provide in the working strength catalystsolution a concentration equivalent to about l()5()0 mg/l of Pd as PdCla stochiometric excess of stannous salt, and a booster compoundconsisting of a soluble metal salt of which the cation is capable offorming a precipitate when contacted with the accelerator solution usedin an electroless plating process employing a substrate which has beencatalyzed in said catalyst solution, said booster compound being presentin amount of about 0.1 mol/l up to 5 mol/l in the working strengthsolution.

8. An aqueous catalytic solution composition as defined in claim 7,wherein the booster compound is selected from the group consisting of CaBa, Fr, 2+ 2+ 2+ m -1+ :i+ 2+ 2+ C 3+ 2+ 2+ 2+ a+

1. A METHOD FOR PREPARING A CATALYST SOLUTION BY HEATING AN ACIDSOLUTION OF A PD(11) CATALYTIC ION WHEREIN SAID CATALYTIC ION IS PRESENTIN AMOUNT SUFFICIENT TO PROVIDE IN THE WORKING STRENGTH CATALYSTSOLUTION A CONCENTRATION EQUIVALENT TO ABOUT 10-500 MG/1 OF PD2+ ASPDCL2, WITH A SOLUTION CONTAINING A STOCHIOMETRIC EXCESS OF STANNOUSSALT WHEREIN AT LEAST ONE OF SAID CATALYTIC ION AND STANNOUS SALTSOLUTIONS IS FIRST HEATED TO A TEMPERATURE IN EXCESS OF 75*C BEFORE THEOTHR IS ADDED TO IT, SND WHEREIN A BOOSTER COMPOUND CONSISTING OF ASOLUBLE METAL SALT, OF WHICH THE CATION IS CAPABLE OF FORMING APRECIPITATE WHEN CONTACTED WITH THE ACCELERATOR SOLUTION USED IN ANELECTROLESS PROCESS, IS ADDED TO THE CATALYST MIXTURE DURINGPREPARATION, SAID BOOSTER COMPOUND BEING PRESENT IN AMOUNT OF ABOUT 0.1MOL/1 UP TO 5 MOL/1 IN THE WORKING STRENGTH SOLUTION.
 2. A method forpreparing a catalyst as in claim 1, for use in an electroless platingprocess employing as the accelerator a strong alkali, wherein thebooster compound is a salt containing a cation selected from the groupconsisting of Mg2 , Fe2 , Fe3 , Mn2 , Mn3 , Cu2 , Ni2 , Co2 , Cr3 .
 3. Amethod for preparing a catalyst as in claim 1, for use in an electrolessplating process employing as the accelerator an alkaline ammoniasolution, wherein the booster compound is a salt containing a cationselected from the group consisting of Mg2 , Fe3 , Mn2 , Mn3 , Cr3 , Pb2, Al3 .
 4. A method for preparing a catalyst as in claim 1, for use inan electroless plating process employing as the accelerator sulphuricacid or a soluble acid sulphate, wherein the booster compound is a saltcontaining a cation selected from the group consisting of Ca2 , Ba2 ,Sr2 , Pb2 .
 5. A method for preparing a catalyst as in claim 1, for usein an electroless plating process employing as the accelerator a solublecarbonate or phosphate, wherein the booster compound is a saltcontaining a cation selected from the group consisting of Ca2 , Ba2 ,Sr2 , Pb2 , Mg2 , Fe2 , Fe3 , Mn2 , Mn3 , Cu2 , Ni2 , Co2 , Cr3 , Cd2 ,Zn2 , Pb2 , Al3 .
 6. A method for preparing a catalyst as in claim 1,for use in an electroless plating process employing as the accelerator asoluble fluoride, wherein the booster compound is salt containing acation selected from the group consisting of Mg2 , Ca2 , Ba2 , Sr2 , Zn2, Cd2 , Al3 , Pb2 , Mn2 , Mn3 .
 7. An aqueous acid catalyst solutioncomprising a Pd(II) catalytic ion wherein said catalytic ion is presentin amount sufficient to provide in the working strength catalystsolution a concentration equivalent to about 10-500 mg/l of Pd2 asPdCl2, a stochiometric excess of stannous salt, and a booster compoundconsisting of a soluble metal salt of which the cation is capable offormIng a precipitate when contacted with the accelerator solution usedin an electroless plating process employing a substrate which has beencatalyzed in said catalyst solution, said booster compound being presentin amount of about 0.1 mol/l up to 5 mol/l in the working strengthsolution.
 8. An aqueous catalytic solution composition as defined inclaim 7, wherein the booster compound is selected from the groupconsisting of Ca2 , Ba2 , Fr2 , Pb2 , Mg2 , Fe2 , Fe3 , Mn2 , Mn3 , Cu2, Ni2 , Co2 , Cr3 , Cd2 , Zn2 , Pb2 , Al3 .